This invention relates to a method and apparatus for measuring and more particularly a method and apparatus for measuring the level of semi-solid material.
Apparatus are known for measuring the level of semi-solid material. The material may be stored in containers such as a closed bin or silo. Mechanical systems are typically employed to determine the level of the material in the containers. The systems usually have a bell or funnel-shaped member, attached to one end of a chain, that is lowered within the container for contacting the surface of the material. Upon contact of the member with the material surface, an indicator attached to the other end of the chain provides visual indication of the level of the material in the container.
One type of prior art measuring device is disclosed in Renkin in U.S. Pat. No. 1,391,504. A conical-shaped block is attached by means of a straight bar and a chain to a manually-operated handle. The handle has an indicator that moves along a height-indicating scale. The chain turns about a sheave located above the container (bin) such that a downward pull on the handle causes the raising of the block within the bin. When it is desirous to determine the level of the material in the bin, an operator pulls the handle downward to a station wherein the block is suspended freely within the bin. The handle is released slowly, and the operator senses the point at which the block contacts the level of the material. At such a point, the level of the material is read from the scale.
The device described in Renkin, however, suffers from several practical problems in that the device must be manually operated, and the block must be in a totally raised position when the bin is being filled with the semi-solid material. In grain storage yards having many silos, for example, manual operation of such measuring devices would be very time consuming, and therefore costly.
Bins using Renkin's device could not be filled while the block is in the lowered position since the weight of the semi-solid material covering the block would prevent it from being raised without excessive force and potential rupture of the cable.
Renkin also describes a tubular member attached to the upper surface of the closed bin for guiding therein the rod attached to the block. Thus, the tubular extension is of a length in the same order as the height of the bin, a highly impractical situation when considering today's storage bins having heights in the order of 125 feet.
Another prior art device is disclosed by Parsons in U.S. Pat. No. 3,629,946. Parsons describes a level measuring device for a container of bulk material. Parsons discloses a reel mechanism coupled to a digital counter, and a weighted bell supporting line that is entrained over sheaves carried by framework on a silo. When it is desired to determine the level of the bulk material in the container, the reel is manually unwound until the bell contacts the material in the container. At such time, the digital counter is read out for conversion to a height indication. Upon completion of the measurement, the reel is rewound, thus, returning the bell to the top of the container where it is locked into place in preparation for a subsequent measurement. Parsons discloses use of plural lines, each line attached to a corresponding container. The reel mechanism and digital counter may be used in conjunction with plural lines so that material level measurement in several containers can be accomplished with the reel mechanism temporarily located at a specific station. As in the other prior art device described, the bell is manually lowered into the container for contacting the surface of the material contained therein. Additionally, the bell must be raised to a position at the top of the silo prior to refilling the silo with the semi-solid material. Thus, Parsons suffers from the same deficiencies as the other prior art device in that manual operation in raising and lowering the bell and its attendant time consumption are present.
Additionally, the use of weights, bells or blocks that are lowered to the surface of the material preclude the use of the measuring device during the unloading as well as loading of the material in the containers. The weight of the reloaded material above the bell would result in stress in the connecting lines causing them to break, and thus, the bell would be carried along with the material removed from the containers.
A device for measuring levels of fluids in containers is described by Beadle in U.S. Pat. No. 2,029,405. The device includes a plurality of serially-connected floats suspended from a spring-loaded height indicator located at the top of a fluid-holding container.
As the fluid in the container is removed, the next serially-connected float becomes suspended thereby causing its weight to be added to that priorly-sensed by the height indicator. The weight of the suspended floats therefore provides an indication of the level of the fluid in the container.
Operation of Beadle's devices relies principally upon the floatation characteristics of the floats upon the surface of the fluid and the weight of the floats suspended above the fluid surface. This technique is not suitable for measurement of semi-solid materials, however, since the floats not suspended would not rest upon the material surface and the downward pull of the material on the floats, that become imbedded within the material, causes inaccurate level measurements as well as potential rupture of the float-suspending cable.